For the purpose of this, you cannot be changing the postal address into a company specific table.
It holds all the addresses (not only vendor). if you really want a separation, you can think of using partitions.

You should have selected to create a different party then rather using the same party?

I didn't meant, you should be using the partition.

AX 2012 initially shipped some of the global data entities like products, global address book, some financial master data...It may not fit every one and every one don't require the data sharing across all entites, so later in R2 they introduced Partition concept in order to have keep them isolated. For more details, see the architecture of it,